A metathesis reaction, in which homologous or heterologous olefins are reacted with each other to yield olefins having different structures, is highly beneficial since the reaction allows interconversion among ethylene, propylene, butene and the like that are produced from naphtha crackers at certain proportions, so as to cope with the changes in the demand structure of olefins.
The olefin metathesis reaction was found in 1931 to proceed at a high temperature of 725° C. without catalyst. However, the industrial value of the reaction was acknowledged only after a catalyst having an oxide of metal such as molybdenum, tungsten, rhenium or the like supported on a large surface area support was found. As the first exemplary metathesis reaction to use catalyst, a method of obtaining ethylene and 2-butene by a metathesis reaction between propylene and propylene using a catalyst comprising molybdenum oxide supported on γ-alumina, was developed by Phillips Inc. in 1964.
The metathesis reaction is reversible, and thus there exists an equilibrium composition. The equilibrium composition of the reaction to obtain propylene from ethylene and 2-butene becomes more advantageous in propylene production as the temperature is lower; therefore, lowering of the reaction temperature by improvement of the catalyst has been examined. Inter alia, a method of using a catalyst comprising tungsten oxide supported on silica and a co-catalyst of magnesium oxide was developed by Phillips Inc., and currently the method has been completed by Lummus Global, Inc. as a process for propylene production.
More particularly, it is reported in U.S. Pat. No. 4,575,575 (Patent Document 1) or Journal of Molecular Catalysis, Vol. 28, p. 117 (1985) (Non-Patent Document 1) that when a metathesis reaction between ethylene and 2-butene is carried out at 330° C. using a fixed bed flow apparatus only in the presence of a catalyst of silica-supported tungsten oxide, the conversion of butene is only 31%, while when magnesium oxide is used in combination as a co-catalyst, the conversion is enhanced to 67%.
Moreover, it is reported in U.S. Pat. No. 4,754,098 (Patent Document 2) that in the same metathesis reaction at 330° C., when a catalyst comprising magnesium oxide supported on γ-alumina is used, the conversion of butene is enhanced to 75%. It is also reported in U.S. Pat. No. 4,684,760 (Patent Document 3) that when a co-catalyst comprising magnesium oxide and lithium hydroxide supported on γ-alumina is used, the conversion of butene can be maintained to be 74% even at a much lower temperature of 270° C. In fact, there are needed facilities such as heating furnace and the like in order to achieve a reaction temperature of 270° C. in the industrial process, and it is desired to lower the reaction temperature to a temperature that is more simply achievable by steam heating, for example, up to about 200° C.
Furthermore, as an example of low temperature reaction catalysts, mention may be made of a catalyst comprising rhenium oxide supported on γ-alumina, developed by IFP (Institut Francais du Petrole). This catalyst is capable of driving the metathesis reaction at a reaction temperature around room temperature, that is, under pressurized conditions, using a liquefied mixture of ethylene and 2-butene as the starting material, as described in U.S. Pat. No. 4,795,734 (Patent Document 4). However, the liquefied raw material and the reaction product have low diffusibility in the pores of the catalyst, and thus deterioration of catalyst activity is severe compared with gas-phase reactions. In addition, since it is not practical to purge the liquefied gas in the reactor at every occurrence of regeneration in order to regenerate the deactivated catalyst, a moving-bed type reactor system in which the catalyst can be continuously withdrawn from the lower part of the fixed-bed reactor system and continuously regenerated has been designed. However, this method also involves complicated installation and has problems in the operational safety.                [Patent Document 1] U.S. Pat. No. 4,575,575        [Patent Document 2] U.S. Pat. No. 4,754,098        [Patent Document 3] U.S. Pat. No. 4,684,760        [Patent Document 4] U.S. Pat. No. 4,795,734        [Non-Patent Document 1] Journal of Molecular Catalysis, Vol. 28, p. 117 (1985)        